Hi Sergey,
I found some keys in the registry that maybe could help you.
First of all, There's many places where you can find the directory of Acrobat but I don't like the idea since the user can change it during installation...
Here's what I found in the registry :
HKEY_CURRENT_USER\Software\Adobe\Acrobat\Version_number
Where Version_number is 5.0 if you have Acrobat 5.0 installed....
I also found many keys like the following :
HKEY_CLASSES_ROOT\AcroExch.Document\AcrobatVersion\
default value : 5.0
I'm not sure it's reliable since I'm not sure of the purpose of the key, but maybe it's a start...
Hope it helps !
Regards